1. Field of the Invention
The present invention relates to a method and apparatus for reproducing a magnetic tape using rotary drum heads preferably applied in, for example, a digital audio tape recorder of rotary head type (R-DAT).
2. Description of the Prior Art
FIG. 1 shows a magnetic tape player 19 in a digital audio tape recorder of rotary head type of a typical prior art device. The magnetic tape player 19 is composed of a rotary drum 2 mounting magnetic heads 3a, 3b having two different azimuth angles, a detecting circuit 10 for sending out a track identification signal HSW in synchronism with the rotation of the rotary drum 2, an equalizer circuit 6, an input circuit 7, a main memory 13, and an output circuit 15. The magnetic heads 3a, 3b mounted along the axis of the diameter, on the side wall of the cylindrical rotary drum 2, scan a magnetic tape 1 obliquely, and read out the information written on the magnetic tape 1. The track identification signal HSW output from the detecting circuit 10 described below, is sent to a servo circuit 11 by way of a line l2. This servo circuit 11 controls the rotation of the motor 12 on the basis of the track identification signal HSW. Consequently, the rotary drum 12 is rotated in the direction indicated by arrow 18.
A detecting element 8, such as a Hall element detects the passing of a magnet 9 built within the rotary drum 2, and sends out a signal, synchronized with the rotation of the rotary drum 2, to the detecting circuit 10. From the detecting circuit 10, for example, a track identification signal HSW is output. This becomes a high level during the period of contact of the magnetic head 3a with the magnetic tape 1, and a low level during the period of contact of the magnetic head 3b with the magnetic tape 1.
The signals from the magnetic heads 3a, 3b are amplified by amplifiers 4a, 4b respectively, and are sent out into terminals Sa, Sb of a changeover switch 5. The changeover switch 5 selectively causes either one of the terminals Sa, Sb to conduct to terminal Sc on the basis of the track identification signal HSW given to the lines l1, l3 from the detecting circuit 10. The terminal Sc is connected to the equalizer circuit 6.
In the equalizer circuit 6, the frequency characteristic of the reproduced signal is adjusted, and the output from the equalizer circuit 6 is given to the input circuit 7.
The input circuit 7 stores the data signal from the equalizer circuit 6 into the main memory 13 through line l4. At this time, in the input circuit 7, an address signal AD1 is supplied to the main memory 13 through line 15 so as to specify the address for storing the data signal. With respect to the data stored in the main memory 13, an error correction circuit 14 specifies an address through line 16. The data of the specified address is read out into the error correction circuit 14 by way of line 17, and a specified error correction process is carried out. The corrected data is sent out from the error correction circuit 14 to the main memory 13 by way of line l7. The corrected data is written into the address specified through line 16. In this way, the data having an error is rewritten into corrected data.
Afterwards, the data of the address specified by an address signal AD2, supplied from the output circuit 15 through line 18, is read out into the output circuit 15 through line l9, sequentially, from the main memory 13. The data being read out is output from the output circuit 15 sequentially as data signal DAOUT.
On the magnetic tape 1, as shown in FIG. 2, tracks Ai (i=0, 1, 2, . . . ) by the magnetic head 3a, and tracks Bi by the magnetic head 3b, are alternately formed.
The R-DAT, when converting an audio signal into a digital signal to record in the magnetic tape 1, changes the sequence of the sampled digital signals, and records on the magnetic tape 1. Such recording a method is called interleaving.
When recording onto the magnetic tape 1, the magnetic tape 1 runs in the direction indicated by arrow 17. When the data L0, L1, L2, . . . , and data R0, R1, R2, . . . at the time of sampling left audio signal and right audio signal are fed in this sequence, such data are recorded on the magnetic tape 1 in the changed sequence as shown in FIG. 2. In the middle of the magnetic tape 1, a parity check code P, which is an error correction code, is recorded together.
For example, when the magnetic head 3a reads out the data from track A1, as shown in FIG. 3(1), the magnetic head 3a reads out the data sequentially, in the running direction of the head during the high level period W2 of the track identification signal HSW. When the magnetic head 3a finishes reading out the data in the track A1, the magnetic head 3b reads out the data written in the track B1 in the next period W3. In this way, the data for the portion of one frame is read out in period W1.
The signal PBSG, which is read out by the magnetic heads 3a, 3b and output from the equalizer circuit 6, is shown in FIG. 3(2). The signal PBSG, from the equalizer circuit 6, is supplied and stored in the main memory 13 together with the address signal AD1 shown in FIG. 3(3) in the input circuit 7.
Concerning the parity check code P mentioned above, at this time, the data are stored in addresses N to N+l, M to M+l, different from the addresses in which data Li, Ri are stored.
The data corrected by the error correction circuit 14 is read out by the output circuit 15. The address signal AD2 output from the output circuit 15 is shown in FIG. 3(5). The data, changed in the sequence by the interleaving as mentioned above, is put back in its initial sequence when the address of the main memory 13 is specified by the address data AD2. In this way, the data signal DAOUT is output in the correct sequence from the output circuit 15 as shown in FIG. 3(4).
In the magnetic tape player 19, the operation of reproducing the magnetic tape 1, while running in the direction as indicated by arrow 16, or so-called reproduction in reverse the direction is explained below. In such a reproduction in the reverse direction, in the period W5 when the track identification signal HSW is at the high level as shown in FIG. 4, the magnetic head 3a reads out the information, for example, from the track A2. Subsequently, in the period W6 when the track identification signal HSW is at the low level, the magnetic head 3b reads out the data in the track B1. In this way, in the period W4, the data for the portion of two tracks is read out. However, it is misunderstood as to form one frame by track A2 and track B1, which are different frame constituent elements. The track identification signal HSW is shown in FIG. 4(1), and the data signal PBSG is given in FIG. 4(2).
The data stored in the specified address in the main memory 13 by the address AD1 shown in FIG. 4(3) is sequentially read out by the address signal AD2 through line l8 from the output circuit 15. The address sequence specified at this time is same as that of reproduction in normal direction mentioned above. The address signal AD2 is shown in FIG. 4(5), and the data signal DAOUT output from the output circuit 15 is shown in FIG. 4(4).
In such a conventional magnetic tape player 19, only by inverting the running direction of the magnetic tape 1, the data is output in the sequence as shown in FIG. 4(2), and thus the data output sequence cannot be inverted. Therefore, in such a magnetic tape player 19, a circuit for further complicated rearrangement of the data sequence is needed, and the construction is unnecessarily complicated. Such additional circuit structure caused an increase in cost.